The present invention relates to sample injectors, in particular in a high performance liquid chromatography application.
In high performance liquid chromatography (HPLC, see for instance http://en.wikipedia.org/wiki/HPLC), a liquid has to be provided usually at a very controlled flow rate (e.g. in the range of microliters to milliliters per minute) and at high pressure (typically 20-100 MPa, 200-1000 bar, and beyond up to currently 200 MPa, 2000 bar) at which compressibility of the liquid becomes noticeable. For liquid separation in an HPLC system, a mobile phase comprising a sample fluid with compounds to be separated is driven through a stationary phase (such as a chromatographic column), thus separating different compounds of the sample fluid.
Valves are commonly used in HPLC applications, for instance injection valves for introducing a liquid sample into a high pressure flowing stream of liquid, a purge valves for positive displacement pumps, flow path switching valves, etc. Such valves used in HPLC applications are often multi-position rotary valves. Examples of multi-position rotary valves are disclosed in U.S. Pat. No. 4,068,528 A (two-position valves) or US 2003/0098076 A1 (multi-function rotary valves or random-access, dual, three-way, rotary switching valves).
Shear valves, which can be used in multi-way embodiments, are usually formed by a housing and a body defining a stepped cavity in which the rotor or seal is positioned. The housing contains at least two shear seal valve members positioned to be aligned with ports in the rotor (body) to establish communication between the shear seal means. Shear valves are usually provided as rotary valves (such as the aforementioned rotary valves) or translational valves (often also called sliding valves), such as disclosed in EP 0321774 A2.
A multi-way switching valve provides a means for selectively routing a fluid input flow to the valve to one of more alternate output flows from the valve. A rotary valve is of the type wherein fluid flow is directed by rotating a valve rotor element to discrete angular positions relative to a stationary valve stator element. A dual rotary valve provides two valves in one valve body, both simultaneously operated by the positioning of the valve rotor. Rotary switching valves are commonly used, for example, in HPLC and other analytical methods to selectively direct a flow stream of one or more fluids along alternate paths to an analytical device or containment vessel.
The aforementioned US 2003/0098076 A1 shows in its FIG. 1 a conventional type of dual, three-way, switching valve 220, which includes a disc-shaped rotor with a set of rotor grooves in the front face of the rotor that contacts, in a fluid-tight manner, the face of a cylindrically shaped stator body at a rotor-stator interface. Inlet passages and outlet passages, longitudinally bored through the stator body to the rotor-stator interface, are selectively fluidly coupled through the rotor grooves corresponding to the rotation of the rotor relative to the stator. Pivoting of the rotor enables the rotor grooves to fluidly couple selected passages of the stator, depending on their placement on the rotor and the angular position of the valve rotor. Model 7030 of Rheodyne, L. P. is an example of this type of switching valve.
WO 2007/109529 discloses methods and apparatus for placing a sample in a chromatographic system. The device and method feature placing samples held in a sample loop to pressurization prior to placing such sample loop in communication with high pressure conduits.
WO 2008/005845 discloses a method for processing a fluid applied to systems that include a valve unit that has a sample-loading state and a sample-introducing state. The sample-loading state disposes a sample loop in fluidic communication with a sample conduit. The sample-introducing state disposes the sample loop in fluidic communication with a process conduit. The method involves transferring a sample through both the sample conduit and the valve unit so that a leading end of the sample exits the valve unit. After transitioning the valve unit to the sample-loading state and allowing the sample loop to decompress, at least some of the transferred sample is loaded into the sample loop. A fluid-processing instrument includes a value unit and a control unit that manages operation of the instrument. The control unit is configured, for example, to implement the above-described method.
WO 2006/083776 discloses a method and apparatus for substantially eliminating destructive transients of pressure or flow rate which can degrade the efficiency and useful lifetime of chromatography columns. The system enables a substantially constant flow of mobile phase liquid to be maintained through the chromatography system by eliminating the flow blockage interval associated with the actuation of sample injection valves. The system further provides a method to reduce the pressure and flow rate transients associated with pressurization of the sample loop contents when the sample loop is introduced to chromatography system delivery pressure.
WO 2006/023828 discloses systems, devices, and methods to mitigate the pressure disturbance associated with the injection of low-pressure analyte samples into a high-pressure HPLC fluid stream, to enhance chromatographic performance related to retention time and reproducibility. An embodiment coordinates the injection run with active pressure control of a binary solvent delivery system to virtually eliminate the customary pressure drop when the low-pressure loop is brought on line. An additional feature is accomplished by forcing a consistent timing relationship between the injection run, the mechanical position of the delivery pump pistons, and the start and subsequent gradient delivery.
US 2007/0251302 discloses a flow path switching valve in which an impact due to the pressure change when a flow path is switched is prevented from being generated. A rotor slot allows an analysis infusion pump to be connected to an analytical column, so as to form a flow path (condensing procedure). The rotor of the flow path switching valve is rotated clockwise for 30 degrees, and the rotor slot allows the analysis infusion pump, the analytical column, and a trap column to be connected. After the pressure in the trap column is raised to the same pressure level as that of the analytical column, the pressure is stabilized, and the pressure difference between the two columns is counteracted (high-pressure procedure). After the pressure between the two columns has been stabilized sufficiently, the rotor is further rotated for 30 degrees, and the trap column and the analytical column are connected in series, so the sample analysis can be performed (dissolution procedure and detection procedure).
In modern HPLC with pressures rising up to 100 MPa and beyond, life time of sample injectors becomes critical, in particular for the injection valve, as a high pressure load acts on the components particularly when switching between a high pressure operation mode and a low pressure operation mode, which causes excessive wear.